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  <div class="question_difficulty">
   难度：Easy
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  <div>
   <h1 class="question_title">
    67. Add Binary
   </h1>
   <p>
    Given two binary strings, return their sum (also a binary string).
   </p>
   <p>
    The input strings are both
    <strong>
     non-empty
    </strong>
    and contains only characters
    <code>
     1
    </code>
    or&nbsp;
    <code>
     0
    </code>
    .
   </p>
   <p>
    <strong>
     Example 1:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> a = "11", b = "1"
<strong>Output:</strong> "100"</pre>
   <p>
    <strong>
     Example 2:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> a = "1010", b = "1011"
<strong>Output:</strong> "10101"</pre>
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   <h1 class="question_title">
    67. 二进制求和
   </h1>
   <p>
    给定两个二进制字符串，返回他们的和（用二进制表示）。
   </p>
   <p>
    输入为
    <strong>
     非空
    </strong>
    字符串且只包含数字&nbsp;
    <code>
     1
    </code>
    &nbsp;和&nbsp;
    <code>
     0
    </code>
    。
   </p>
   <p>
    <strong>
     示例&nbsp;1:
    </strong>
   </p>
   <pre><strong>输入:</strong> a = "11", b = "1"
<strong>输出:</strong> "100"</pre>
   <p>
    <strong>
     示例&nbsp;2:
    </strong>
   </p>
   <pre><strong>输入:</strong> a = "1010", b = "1011"
<strong>输出:</strong> "10101"</pre>
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